Treatment of synthetic fiber tow



March 1963 M. WISHMAN 3,083,071

TREATMENT OF SYNTHETIC FIBER TOW Filed Dec. 21, 1959 I I I 5O 6O (W T.) CH COOH 39V |NIHHS INVENTOR. MARVIN WISHMAN BY fiat/7K ATTORNEY United States Patent 3,083,071 TREATMENT OF SYNTHETIC FIBER TOW Marvin Wishman, White Plains, N.Y., assignor to American Cyanamid Company, New York, N.Y., a corporation of Maine Filed Dec. 21, 1959, Ser. No. 861,115 Claims. (Cl. 8-1301) This invention relates to a new process for relaxing acrylic fibers. More particularly the invention relates to a method of relaxing acrylic fiber tow which comprises treating the tow with acetic acid.

In order to improve the physical properties of synthetic fibers which are produced by both the wet and dry processes, it is the custom to take the newly produced fiber tow and send it through a series of treatments which include washing to remove the solvent, stretching to orient the molecules in the direction of the axis of the fiber, drying (if it has not previously been dried), and then finally relaxing the fiber tow so that desired physical properties are obtained. This relaxation is manifested by an actual shrinkage of the fiber. All of the above steps are necessary in order to obtain a fiber or filament which has both the desired physical and chemical properties usually considered necessary for use in textiles. The relaxing or shrinkage step is very critical because it is this step which helps control the fiber dye receptivity and its strength characteristics; and also because this is the process step in which the desired denier is obtained.

Many methods have been used in the prior art to obtain relaxation of synthetic fiber tow. Some of these are boiling in water, treating with steam at elevated temperatures and pressures and treating with chemical agents such as solvents and chemicals which tend to swell the fibers.

All of these relaxing means have decided disadvantages. Boiling the fiber tow in water does not usually give sufiicient shrinkage or relaxation to the fiber for obtaining the desired strength properties and dye receptivity which are needed for use in textiles. Treating the fiber tow with steam at elevated temperatures and pressures can provide the necessary shrinkage or relaxation but is often harmful to fiber color and, therefore, is undesirable from that standpoint.

The use of other agents such as weak solutions of solvents and chemicals that tend to swell 'the'fiber is very effective for the shrinkage and relaxation of acrylic fiber tow. However, it is difficult to maintain control over the concentration of these solvents and chemicals in order to obtain the exact degree of shrinkage. Another disadvantage in the use of these materials is the fact that they are frequently preferentially adsorbed by the fiber. Excessive washing is required in order to remove their combined residue if they can be removed at all.

Applicant has unexpectedly and surprisingly found that he can avoid all of the undesirable features of the abovementioned relaxing means by treating fiber tow vw'th acetic acid aqueous solutions. After relaxation in acetic acid aqueous solution the fiber tow manifests improved loop tenacity, loop elongation and dye receptivity over that obtained when water alone is used. There is no problem with fiber color as when steam treatment is used to relax the fiber tow. The acetic acid treatment has a decided advantage over the solventand swelling-chemical-type treating agents in that changes in concentration may be more easily regulated and also the fact that acetic acid is not preferentially adsorbed by the fiber.

Applicant is unable to explain why acetic acidlworks as a relaxing agent at all in the treatment: of polyacrylonitrile filamentary material produced by known wetor dry-spinning methods, since it is not a solvent or does not tend to swell the fiber when used in any concentration.

3,083,071 Patented Mar. 26, 1963 Other chemicals which aid in shrinking or relaxing fibers inevitably either dissolve or swell the fibers when used in suificient concentrations. Therefore, if one were to seek a new shrinking or relaxing agent, he would test all chemicals which were known to dissolve or swell the fibers to be rel-axed. The use of N,N-dirnethylformamide as a shrinking agent, which is a well-known solvent for polyacrylonitrile and other acrylic copolymers, is disclosed in US. Patents 2,821,458, 2,404,7l4-2,404,727, and 2,716,- 586.

Another novel feature in the use of acetic acid as a shrinking or relaxing agent is the fact that'maximium shrinkage is obtained with intermediate concentrations which do not vary the shrinkage obtained for a substantial range of concentrations at this maximum. This phenomena is also unexplainable since the percent shrinkage drops after'a certain maximum concentration. Inasmuch as the other well-known shrinking agents influence the shrinking of the fibers in a direct line relationship, this feature is totally unexpected and surprising.

One object of this invention is to provide a new method for relaxing synthetic acrylic fiber tow.

It is another object of this invention to provide a new method for relaxing synthetic acrylic fiber towwithout the use of excessive heat or pressure.

It is still another object of the invention to provide a newmethod for relaxing synthetic acrylic fiber tow which is easily controlled.

The single FIGURE of the accompanying drawing is .a graph plotting the percentage of'shrinkage of the fiber tow versus the concentration of acetic acid; the several curves define relationships obtained at different temperatures.

The invention is carried out on a synthetic acrylic fiber tow, which has been stretched to a definite degree, by treating the said tow with a definite concentration of' acetic acid in water at definite temperatures. The thusly treated tow is then washed and dried. Applicant has found that by controlling the temperature of the treatment or by varying the acetic acid concentration, different degrees of shrinkage are obtained. The length of time that the fiber is treated has ,been found to be critical only in that the fiber must be in contact with the acetic. acid solution for a minimum duration. After this minimum duration is observed, the process is considered to be non-dependent on time. In the figure it is easily seen that the shrinkage of the fiber varies considerably with the concentration of acetic acid except where maximum shrinkage is obtained at about 70 weight percent concentration. This graph shows that the amount of shrinkage of the synthetic acrylic fiber varies in almost straight line relationship from 0% concentration to about 60% concentration. From 60 to 77% concentration there is less than 1.0% change in: shrinkage. As the concentration increases above 77%, there is a sharp drop in the shrinkage obtained with the synthetic fiber tow. Since the maximum shrinkage is obtained with a substantial variance in the concentration of acetic acid, namely 17% concentration, a treating solution anywhere within this range gives, essentially constant shrinkage of the fiber.

The following examples are give-n by way of illustration and not by way of limitation. All quantifies are given'in parts by weight unless otherwise designated.

EXAMPLE 1 A copolymer containing acrylonitrile/Z-methyLS-vinylpyridine/vinyl acetate (89/6/5) is wet spun from an aqueous sodium thiocyanate solution into a cold, aqueous coagulating bath as is described more fully in, for-instance, Cresswell Patent No. 2,558,730, dated July: 3, 1951, to produce a 16,800 denier-1000 filament tow-whichis hotwet drawn eight times its original length to produce a tow of about 2,100 denier. The tow is then dried under controlled temperature and humidity conditions, so that a compact, collapsed structure is formed.

Measured lengths of this tow are subjected for 0.5 hour at 98 C. to aqueous solutions containing varied amounts 'of acetic acid. The treated tow samples are washed with water at room temperature until the odor of acetic acid is gone and are then dried in air at 30 C. The final length is determined and the percent shrinkage determined as where L is the original length The data are found in Table I.

Table I and L is the final length.

Gone. acetic acid (by Weight) 40. 4 Percent shrinkage Lo-Lf/ LOXIOO The data are plotted as the top curve of the accompanying figure. 7

Fiber shrinkage occurs to the greatest extent (about 40%) at acetic acid concentrations between 60 and 80%. There is very little variation in the amount of shrinkage with change in acetic acid concentration between 60 and 80%. Use of deionized Water at 98 C. is found to cause shrinkage of about 5%, while glacial acetic acid causes a shrinkage of only 17.0%. It is most unexpected that a maximum in shrinkage should be obtained through the use of a mixture of two relatively poor shrinkage agents, i.e., water and acetic acid at 98 C.

EXAMPLE 2 Dried and collapsed tow, prepared as described in Example 1, is subjected for 0.5 hour at 98 C. to aqueous solutions containing varied amounts of acetic acid. After thorough washing with deionized water, the fibers are dried in air at 30 C. Fiber properties are determined. The relative rate of dye absorption of the resultant fiber for an acid-type dye such as Acid Blue 45" is determined by placing a skein of the subject yarn and a skein of a competitive standard in a boiling, aqueous bath at pH 2.0-2.2 for one hour. The bath contains 1% dye on the weight of fiber, and the liquor/fiber ratio is 50/1. The dye uptake is rated by visual comparison with the standard considered to be 100%. The efiect of the treatment on the dried and collapsed tow with varying concentrations Of acetic acid is manifested by the data of the following Table II.

Table 1 From the data in Table II it can be seen that straight tenacity decreases and straight elongation increases as the acetic acid concentration approaches -80%. At the same time the loop properties become more nearly like the straight properties as shown by the increase in the ratio of these properties with treatment with acetic acid. The relative rate of dyeing improves with use of acetic acid in the shrinking medium. When either water or acetic acid alone is used the ratios of loop/straight tenacity and loop/ straight elongation are low, indicating that the fiber is brittle and loses strength in bending. These ratios improve with treatment 111 aqueous acetic acid solution.

EXAMPLE 3 Dried and collapsed tow is subjected for 0.5 hour to aqueous solutions containing varied amounts of acetic acid as described in Example 1, except that the temperature of the treatment is varied from to 98 C. These data are found in Table III. The data are more conveniently seen in the accompanying figure.

' Table III SHRINKAGE RESULTS OBTAINED FROM AOETIO ACID TREATMENT OF DRIED AND OOLLAPSED TOW MADE FROM A OOPOLYMER or AORYLONITRILE/2-METHYL- S-VINYLPYRIDINE/VINYL ACETATE (8916/5) WHERE THE TEMPERATURE AND THE CONCENTRATION on THE ACETIG ACID Ann VARIED Acetic acid con- Percent shrinkage at varied temperatures centration (by weight) 75 C. 0. C. C. 98 C.

1.0 V 2. 5 7. 0 13. 0 17.5 '9. 0 18.0 21.0 24. 5 30. 5 15. 5 18. 0 .23. 0 27. 5 34. 5 19. 0 22. 5 27. 0 31. 5 39. 0 20.0 24. 0 28. 5 38. I) 41. 0 18. 5 22. 5 27. 0 32. 0 40. 5 17.0 20. 5 V 24. 5 29. 0 87.5 11. 5 15. 0 17. 5 21. 5 30. 0 3.5 .6. 0 9. 0 12. 0 17. 0

It is seen that at each temperature employed the amount of fiber shrinkage which occurs is at a maximum when 65-75% acetic acid, by :weight, is used. For instance, despite the fact that the tow does not shrink in either water or glacial acetic acid at 75 C., the tow shrinks 20% when 65-75% acetic acid solutions are used.

Equivalent amounts of shrinkage are obtained at an infinite vaniety. of temperature and acetic acid concentration conditions. EXALIVIPLE 4 The data in the accompanying figure show that many difierent conditions of treatment, acetic acid concentration and temperature can be employed to obtain the same amount of shrinkage with a sample of tow. A dried, collapsed tow of about 2,200 denier-1000 filaments is AND COLLAPSED TOW MADE FROM A COPOLY- V AGRYLONITRILE/2-METHYL15-VIN YL PYRIDINE/VINYL ACETATE (SQ/ 6 5) WITH TREATMEN T IN VARIOUS CONCENTRATIONS OF ACETIQ ACID Ratio of Ratio 0! Cone. acetic acid (by Percent Straight Straight Loop Loop loop to loop to Dye ratweight) fiber tenacity elongatenacity elongastraight straight mg shrinktion tion tenacity elongaage tion None (water only) 6. 0 3. 4 39. 5 1. 4 14. 0 41 35 5 treated -for 0.5 hour at seven different conditions predicted to yield about 27% shrinkage so that 3,000 denier- 1000 filament tow will result. The conditions used and the resultant fiber properties are found in Table IV.

Table IV 6 and a 60,000 denier tow (3 d./fil.) should result. The rate of introduction of fiber into the relaxation tube is such that the storage space in the curved portion of the tube permits a treatment time of 15 minutes. The physi- THE FOLLOWING DATA ILLUSTRATE THE LARGE DEGREE OF CONTROL OF FIBER PROPERTIES WHICH CAN BE OBTAINED BY THE ACETIC ACID TREATMENT Temper- Percent Ratio of Ratio of Gene. of ature, 0. her Straight Straight Loop Loop loop to loop to acetic acid of acetic shrinktenacity elongation tenacity elongation straight straight acid age tenacity elongation (The data in Table IV show that wide acetic acid variations do not result in fibers of difierent physical properties as long as the treatment is conducted with 60-80% acetic acid. When the acetic acid concentration is lower or higher than the 60-80% range, but the operating temperature is adjusted so that the same shrinkage is obtained, in each case the properties of the resultant fibers are very nearly the same.

EXAMPLE 5 A copolymer containing acrylonitrile and methyl/acrylate (90/ 10) is spun to dry, collapsed tow in the manner described in Example 1, except that the denier of the tow is 2.5 denier/filament rather than 2.1 denier/ filament.

The tow is then treated in aqueous solutions of varied acetic acid concentration for 0.5 hour at 100 C. The data are found in Table V.

Fiber shrinkage in acetic acid solution is at a maximum when 50-80% acetic acid is used.

Table V CHANGES IN PROPERTIES OF TOW MADE FROM A COPOLYMEB, CONTAINING AC'RYLONITRILE/ METHYL ACRYLATE (SO/10) WITH TREATMENT IN VARIOUS CONCENTRATIONS OF ACETIC ACID Percent acetic acid Percent Final Loop Loop by weight shrinkage denier tenacity elongation Under these conditions fiber brittleness, as measured by loop tenacity and elongation, are improved. Again,

solutions containing intermediate concentrations of acetic acid are more effective than either water or acetic acid alone. 1

EXAMPLEfi A copolymer containing acrylonitrile-Z-rnethyl-S-vinylpyridine/ vinyl acetate (89/ 6/5) is wet spun from aqueous sodium thiocyanate to produce a 30,400 denier-200 0 filament which is stretched to eight times its original length through hot water and dried at controlled temperature and humidity conditions so that a compact, collapsed structure is formed. The total denier at this point is 4,800 or 2.4 denier per filament. This tow is introduced continuously into a glass tube shaped like the letter J, while a solution of 77% acetic acid at 77 C. is introduced in acountercurrent direction. From the accompanying figure it is seen that 20% shrinkage is expected cal properties of this fiber are found in the first column of Table VI. 4

Table VI Fiber Fiber Fiber Tested physical properties of treated treated treated the fiber in 77% in water in water acetic acid at 98 C at 115 C.

Denier! filament 3.0 2. 7 3. 1 Straight tenacity (g./d.) 2. 7 3. 4 2. 9 Straight elongation (percent) 48. 5 35. 5 49. 0 Loop tenacity (g./d.) 1. 5 1.0 1.8 Loop elongation (percent) 28. 0 3. 5 30.0 Inltial modulus (g./d 58.6 57. 0 41. 5 Compliance ratio 94 45 .50 Fiber yellowness 0. 099 0. 102 0.139 Acid dyeability 120 50,

Fiber yellowness is obtained from the following calculation: The (inference between the percent reflectance at 050 millimicrons wave length and at 430 millimicrons in divided by the percent reflectance at 550 millimicrons. The quotient of this value and 1.57 is equal to fiber yellowness.

Some of the dried, collapsed fiber is treated with water at 98 C. for 15 minutes or with water at C. for 15 minutes. In order to obtain a temperature of 115 C., it is necessary to operate at a pressure of 1.66 atmospheres absolute. The properties of these fibers are found in columns 2 and 3, respectively, of Table VI.

From the data in Table VI it is seen that fiber which is shrunk in water at 98 C. has low loop tenacity and low elongation. Fiber dyeability is poor compared to the samples in columns 1 and 3. The loop properties of the fibers which are shrunk to approximately 3.0 denier in 77% acetic acid at 77 C. or water at 115 C. indicate that these samples are not brittle. In order to operate at 115 C. in water, pressures above atmospheric are required and special equipment is needed. Fiber yellowness is afiected by treatment at elevated temperature as is indicated by the data in Table VI. The least yellow fiber is that obtained upon treatment with acetic acid.

The initial modulus and compliance ratio of the fiber that is shrunk in acetic acid are of great interest. It is usually found (compare columns 1 and 2) that the initial modulus decreases and the compliance ratio increases when the fiber is shrunk. The initial modulus does not change but the compliance increases when the fiber is shrunk in acetic acid.

EXAMPLE 7 Shrinkage of fiber prepared as described in Example 1 may be accomplished by use of other agents. Most of these agents will swell or dissolve the acrylic fiber if not diluted with a non-solvent suchas water. However, when the concentration of the agent used is varied the amount of shrinkage obtained varies. There are no conditions under which shrinkage does not vary when the concentration of the agent varies as is found when 60-80% acetic acid is used.

The dried, collapsed tow is treated with water at 98 C. and is then dried at 30 C. This fiber is then treated 60% and 77%). e

7 with varied agents diluted with water to varied con centrations in order to find the amount of shrinkage obtained above that in water at 98 C. The results are found in Table VII. 1

Table VII 'ltemperia- Shrinking agent used Time Percent i f (hrs) shrinkage 10% formic acid, 90% water S0 0. 8 30% formic acid, 70% water" 80 0. 5 32 50% formic acid, 50% water 80 0. 5. 70 77% formic acid, 23% water 80 0.5 acetonitrile, 90% water 70 0.5 3 25% acetonitrile, 75% water 70 0.5 19 50% acetouitrile, 50% water 70 0.5 53 75% acetonitrile, 25% water 7 0 0.5 100 o acetonitrile 70 0.5 30 o acetic acid, 70% water 95 0.5 6 40% acetic acid, 60% water. 95 0.5 10 50% acetic acid, 50% water.-. 95 0. 5 16 60% acetic acid, 40% water. 95 0. 5 21 70% acetic acid, 30% water. 95 0. 5 22 80% acetic acid, 20% water. 95 0. 5 21 90% acetic acid, 10% water- 95 0.5

1 Dissolves. 2 Fiber fused.

From the data in Table VII it can be seen that there is little difierence in the amount of shrinkage which results when the fiber is treated with 60%, 70% or 80% acetic acid solution and that the amount of shrinkage obtained at these concentrations is greater than that obtained when either more or less concentrated solutions are used as the shrinking medium. When formic acid or acetonitrile is used the amount that the fiber shrinks increases with increasing concentration of the agent, and solution or fushion of the fiber results at high concentrations of the agent. 7

The invention may be used with any fiber or filamentary material made from a polymer of acrylonitrile having combined in the polymer molecule at least 80% by weight acrylonitrile. Typical of the polymers which are operative is one comprising 85% acrylonitrile, 7 /2% Z-methyl-S-vinylpyridine and 7 /2% vinyl acetate. Another typical polymer is one comprised of 95% acrylonitrile and 5% methyl a'crylate. Other comonomers which may be used with acrylonitrile in the preparation of these I claim:

1. The method of relaxing dried filamentary material comprised of a polymer selected from the group consisting of (1) homopolymeric acrylonitrile and (2) thermoplastic copolymers of acrylonitrile having combined in the copolymer molecule at least 80% by weight of acrylonitrile, the remainder being at least one other different monoethylenically unsaturated monomer which is copolymerizable with acrylonitrile, said method comprising treating the said dried filamentary material with an aqueous acetic acid solution containing from 50% to 80% by weight of acetic acid at an elevated temperature, the degree of relaxation being a function of said elevated temperature.

2. A method as in claim 1 wherein the polymer of which the filamentary material is comprised is a thermoplastic copolymer of acrylonitrile as defined under (2) of claim 1, and the period of treatment is at least one minute.

3. A method as in claim 1 wherein treating is effected by passing the defined filamentary material through a solution containing from 60% to 77% by weight of acrylic-type polymers are acrylic acid, methylacrylic acid,

other vinyl-type compounds such as vinyl chloride, vinyl pyridines, styrene and derivatives thereof, allyl compounds such as allyl alcohol, allyl-substituted benzene compounds and the various allyl pyridines; Qther examples of monomers which are copolymerizable with acrylonitrile to form fiber-forming polymers fromwhich can be made filamentary materials that can be treated in accordance with the present invention are given in,

for example, US. Patent No. 2,874,446, more particu-- larly in the paragraph beginning in column 4, line 57, and ending in line 12 of column 5. As has been indicated hereinbefore, homopolynieric acrylonitrile alone can be the fiber-forming polymer; or one can use thermoplastic copolymers of acrylonitrile, more particularly 1 acrylonitrile copolymers having combined in the polymer molecule at least 80% by weight of acrylonitrile, e.g., from about 85% to 90%, and up to 20%, e.g., from about 10% to 15%, by weight of atleast on'e'(e.g., 2, 3, 4 or any desired number) other, different monoethylenically unsaturated monomer (e.g., one containing, a CH =C grouping) which is copolymerizable' with acrylonitrile. In the use of every one of thesepolymers with acetic acid the maximum shrinkage obtained is with acetic acid of about 70% concentration (between The curvature of the graph 'is'of the same contour for every polymer but is at a different peak. Also by v changing the temperature, the peak valuesfmay be chang but the contour remains the same.

acetic acid for a period of at least one minute.

4. A method as in claim 1 wherein the temperature of the aqueous acetic acid solution with which the filamentary material is treated is between about C. and about 98 C.

5. A method of controlling the shrinkage of dried filamentary material comprised of a polymer of acrylonitrile as defined under (2) of claim 1, said method comprising contacting the said filamentary material, for a period of from 1 to 30 minutes, with an aqueous solution of acetic acid containing between 60% and 77% by Weight of said acid while maintaining the temperature of said solution between about 75 C. and about 98 C.

6. A method as in claim 1 in which the polymer contains combined in the polymer molecule, from about to by weight of acrylonitrile and from about 10% to 15% by weight of at least one other different monoethylenically unsaturated monomer which is copolymerizable with acrylonitrile and which contains a CH =C grouping.

7. The method of claim 1 in which the polymer contains, by weight, about 89% acrylonitrile, 6% Z-methyl- 5-vinyl pyridine and 5% vinyl acetate combined i h polymer molecule.

, References Cited in the file of this patent UNITED STATES PATENTS 2,431,956 Moody Dec. 2, 1947 2,848,296 Heller Aug 19, 1958 2,853,483 7 Rhyner Sept. 23, 1958 V V FOREIGN PATENTS.

614,009. Great Britain Dec. 8,1948

Great Britain July 15, 1959 'OTHER REFERENCES Du PontTextile Fibers Technical Bulletin OR-54, June 1955, 6 pp. 

1. THE METHOD OF RELAXING DRIED FILAMENTARY MATERIAL COMPRISED OF A POLYMER SELECTED FROM THE GROUP CONSISTING OF (1) HOMOPOLYMERIC ACRYLONITRILE AND (2) THERMOPLASTIC COPOLYMERS OF ACRYLONITRILE HAVING COMBINED IN THE COPOLYMER MOLECULE AT LEAST 80% BY WEIGHT OF ACRYLONITRILE, THE REMAINDER BEING AT LEAST ONE OTHER DIFFERENT MONOETHYLENICALLY UNSATURATED MONOMER WHICH IS COPOLYMERIZABLE WITH ACRYLONITRILE, SAID METHOD COMPRISING TREATING THE SAID DRIED FILAMENTARY MATERIAL WITH AN AQUEOUS ACETIC ACID SOLUTION CONTAINING FROM 50% TO 80% BY WEIGHT OF ACETIC ACID AT AN ELEVATED TEMPERATURE, THE DEGREE OF RELAXATION BEING A FUNCTION OF SAID ELEVATED TEMPERATURE. 